This invention relates generally to photographic printing apparatus, and more particularly to such apparatus which is capable of automated exposure of photosensitized plates to light using both masks and films.
This present invention represents a modification of the apparatus shown in co-assigned U.S. Pat. No. 4,423,955. This apparatus provides for the automated exposure of photosensitized (lithographic) plates to light through films, and is particularly for use in newspaper printing operations to expose plates to light through photographic negatives of the newspaper pages. The apparatus described in the patent is not equipped for automated handling of masks. It will be noted in this regard that masks are commonly used in the processing of plates used in commercial printing applications, such as plates used in the printing of books and magazines. Such processing involves placing a plate, a film and a mask in superposed relation at an exposure station (with the film overlying the plate and the mask overlying the film), lowering a vacuum frame ("window") over the superposed sheets, and exposing the plate to light through the mask and film. An attempt has been made to automate this process by using apparatus substantially of the type described in U.S. Pat. No. 4,423,955, but modified so that the vacuum frame raises both the mask and the film off the plate after exposure of the plate is complete. In this modified apparatus, a discharge carriage travels to the exposure station, grips the plate and the film, and carries both to a discharge station where the plate and film are discharged. The carriage then returns to the exposure station for pickup and conveyance of the mask to the discharge station. This process is inefficient and further has required that the film be larger in size than the mask (to permit a mask and film to be simultaneously raised by the vacuum frame), which is typically not the case unless the film is reduced in size prior to the process.
There is a need, therefore, for apparatus for automating the exposure of lithographic plates when masks are involved.